Biomechanical Validation of Medial Pie-Crusting for Soft-Tissue Balancing in Knee Arthroplasty William M. Mihalko, MD, PhD a , Erik L. Woodard, MS a , Casey T. Hebert, MS a , John R. Crockarell, MD a , John L. Williams, PhD b a University of Tennessee-Campbell Clinic Department of Orthopaedic Surgery & Biomedical, Engineering, Memphis, Tennessee b University of Memphis Department of Biomedical Engineering, 330 Engineering Technology Building, Memphis, Tennessee abstract article info Article history: Received 29 July 2014 Accepted 5 September 2014 Available online xxxx Keywords: total arthroplasty varus knee gap balancing pie-crusting technique cadaver biomechanical study Balancing a varus knee is traditionally accomplished by releasing the medial soft-tissue sleeve off the tibia. Re- cently, “pie-crusting” (PC) medial structures has been described. In a biomechanical cadaver study we compared PC to traditional release (TR) to determine their effects on flexion and extension gaps. PC was done in five spec- imens along the anterior half of the medial soft-tissue sleeve and five along the posterior half, followed by a tra- ditional release. In 90° flexion, valgus laxity after TR was significantly greater than after PC alone. PC of the anterior or posterior aspect of the medial soft-tissue sleeve can effect changes more in flexion than in extension, respec- tively. Complete TR did not provide more gap opening than PC in extension, but produced more effect in flexion. © 2014 Elsevier Inc. All rights reserved. Soft-tissue or gap balancing is an important part of total knee arthroplasty (TKA) surgery, especially in osteoarthritic knees with varus deformity. Traditionally, balancing has been done by subperiosteally releasing portions of the medial soft-tissue sleeve off the proximal tibia [1–13], but this may lead to excessive laxity (especially when the posterior cruciate ligament is sacrificed) or residual pain about the area where the release was done [4,10,13–17].A “pie-crusting” (PC) or “inside-out” technique has been described to balance the varus knee without compromising the structural integrity of the ligamentous struc- tures and without subperiosteal (traditional) release [1,5,6,18–24]. Compared to isolated releases along the posterior aspect of the proximal tibia, releasing the anterior aspect of the medial soft- tissue sleeve may produce a larger increase in the joint gap in flexion than in extension [11,23]. Whiteside et al [11] compared the effects of a traditional release of the anterior portion of the medial collateral ligament (MCL) to the effects of release of the posterior aspect of the MCL and the posterior oblique ligament and found that anterior release had a greater effect on the flexion gap while the posterior release affected mainly the extension gap. If pie-crusting techniques on the medial side of the knee can obtain equal effects in flexion and extension, there would be obvious advan- tages over complete ligament release. The purposes of this study were to determine what parts of the medial soft-tissue sleeve affect the gap in flexion or extension and to compare the results of pie-crusting to an additional standard medial release [4]. Our hypothesis was that pie crusting would be as effective as a traditional subperiosteal release and that targeting the anterior and posterior aspects of the medial soft-tissue sleeve would have more effect on the flexion and extension gaps, respectively. Material and Methods The specimens used in this study were lower extremities from fresh cadavers of donors who had undergone a previous primary TKA (Medical Education and Research Institute, Memphis, TN, and Restore Life USA, Johnson City, TN). IRB approval was obtained before beginning the study. Fourteen knee specimens (5 left and 9 right) were retrieved and all skin, subcutaneous tissue, and muscle were removed, while all aspects of the knee capsule and surrounding ligaments were carefully retained. Each specimen underwent fluoroscopic imaging to confirm no signs of aseptic loosening or bearing wear was present. The femur and tibia were cut transversely 180 mm proximal and distal to the knee joint line, the proximal tibio-fibular joint was left intact, and the fibular shaft was transected 100 mm from the joint line. The femur and tibia of each specimen were potted with urethane epoxy (Goldenwest MFG Inc, Cedar Ridge, CA) in a coupling that allowed mounting into a custom knee testing machine that has been validated in previous studies (Fig. 1) [11,17,23]. Specimens were placed with the tibia mounted The Journal of Arthroplasty xxx (2014) xxx–xxx All research for this study took place at the University of Tennessee-Campbell Clinic Dept. of Orthopaedic Surgery & Biomedical Engineering. Each author certifies that he has no commercial associations (eg, consultancies, stock ownership, equity interest, patent/licensing arrangements, etc.) that might pose a conflict of interest in connection with the submitted article. The Conflict of Interest statement associated with this article can be found at http:// dx.doi.org/10.1016/j.arth.2014.09.005. Reprint requests: William M. Mihalko, MD, PhD, University of Tennessee-Campbell Clinic Department of Orthopaedic Surgery & Biomedical, Engineering, 1211 Union Avenue, Suite 510, Memphis TN 38104. http://dx.doi.org/10.1016/j.arth.2014.09.005 0883-5403/© 2014 Elsevier Inc. All rights reserved. Contents lists available at ScienceDirect The Journal of Arthroplasty journal homepage: www.arthroplastyjournal.org Please cite this article as: Mihalko WM, et al, Biomechanical Validation of Medial Pie-Crusting for Soft-Tissue Balancing in Knee Arthroplasty, J Arthroplasty (2014), http://dx.doi.org/10.1016/j.arth.2014.09.005